Sockets for removably mounting an electronic package on a circuit board or other substrate are well-known. An electronic package having terminal pins, or leads, is typically mounted on a socket having contacts with resilient arms which are deflected by the pins upon full insertion of the package, and the package is secured to the socket by frictional resistance of the contact arms acting on the pins.
A particular type of electronic package known as a pin grid array (PGA) package has terminal pins arranged in an array and extending away from a face of the package. Due to the relatively large number of pins associated with a PGA package, frictional resistance to insertion and extraction of the pins into and from a socket is generally quite large. In order to facilitate the socketing of PGA packages, zero insertion force (ZIF) PGA sockets have been developed examples of which are disclosed in U.S. Pat. Nos. 4,498,725 and 4,988,310 which are owned by AMP Incorporated of Harrisburg, Pa. These sockets have a base which houses an array of contacts, and a cover with a corresponding array of openings which is slidable on the base. When the cover is an open position relative to the base, the pins of the PGA package are insertable through the openings in the cover and into respective cavities in the base without encountering insertion resistance. When the cover is moved to a closed position, the pins are translated within their cavities so as to deflect arms of their associated contacts, thereby securing the package to the socket by frictional resistance. Movement of the cover back to the open position retracts the pins from engagement with the arms and thereby releases the package for removal.
The cover has two main purposes. One is to align the pins with the openings of their respective cavities so that the pins will enter clear portions of the cavities which are unobstructed by contacts. Another purpose is to provide a vehicle for translating the package across the top surface of the base so that the pins become engaged with their contacts. Although the cover serves these purposes, it also has drawbacks in that it increases the size, cost and complexity of the socket assembly. Further, the cover is generally actuated with a cam which is housed in a pocket between the base and the cover, and an actuation lever which is connected to the cam and exposed on a side of the socket. The cam and lever take up additional space and further increase the size and cost of the socket, and pose complexity in assembly of the socket. Due to the constant emphasis on miniaturization in modern technology, a ZIF socket which does not have a cover would be desirable.
ZIF sockets are also subject to accidental misuse by personnel that attempt to install a PGA package when the lever arm, and therefore the cover, is in the closed position. This problem has occurred even at manufacturer locations where proper training in procedures for installing PGA packages into ZIF sockets is supposedly provided. With the advent of a computer industry strategy which encourages end users to swap microprocessors in order to upgrade their machines, it is even more likely that PGA packages will be incorrectly applied to closed ZIF sockets. A ZIF socket which does not have a movable cover would overcome this problem.